In the drive for higher integration in integrated circuitry, it is desired to form patterns to finer feature sizes. Chemically amplified resist compositions are believed promising to this end. The light source used for exposure is typically high-energy radiation such as UV, deep UV and electron beams as disclosed in U.S. Pat. Nos. 4,491,628 and 5,310,619 (JP-B 2-27660 and JP-A 63-27829). The electron beam lithography is not only of interest as the microprocessing technology capable of patterning to a feature size of 0.1 μm or less, but also becomes indispensable to form mask patterns.
However, electron beam imagewise writing takes a longer time than the conventional block exposure process. To increase the throughput, resists are thus required to have a higher sensitivity. The stability with time of resist in vacuum during and after imagewise writing is also one of crucial performance factors. Some coatings on substrates, for example, coatings (e.g., SiO2, TiN, Si3N4) on silicon wafers and chromium oxide on mask blanks can affect the resist profile after development depending on the particular type of substrate. For achieving high resolution and maintaining a profile after etching, it is one of important performance factors that the pattern profile of resist is kept rectangular independent of the substrate type.
Reference is also made to JP-A 11-249309.